Prior to the advent of the present invention, conventional metal electrical junction boxes have been four inches square (i.e., four inches on a side) and two and one-eighth inches deep. In approximately 1978, fire alarm signaling devices of the type including both a strobe light and either an audio speaker or chimes, sometimes called a speaker-strobe or chime-strobe, were introduced; and the four inch by four inch by two and one-eighth inch deep boxes were inadequate in size to accommodate the unit and the electrical conductors necessary to power the unit. Accordingly, the industry began to use an extended version of the box, as shown in FIG. 1. That extended version includes a conventional four inch by four inch by two and one-eighth inch deep junction box 1 having a four inch by four inch by one and one-half inch extension 2 connected thereto via screws 3. The forward end of the extension 2 is provided with flanges 4 for mounting the alarm signaling unit thereto. However, this extended four inch square combination unit has proved to be inadequate, for several reasons. First, the space inside the extended junction box is inadequate, considering the necessity of containing both alarm signaling unit and various electrical conductors that must be accommodated in the box for powering the particular alarm signaling unit and other components in the system in which the alarm signaling unit is installed (e.g., other alarm signaling units and/or other electrical devices down the line). The extension unit cannot be made any deeper than one and one-half inches because the combined depth of the two and one-quarter inch deep (outside dimension) four square junction box and a one and one-half inch deep extension is the maximum that will fit in the three and one-half inch conventional stud space when mounted on a bar hanger. In fact, that combined depth of three and three-quarters inches causes a small but undesirable bow on the back side of the wall when mounted on a bar hanger. Furthermore, as shown in FIG. 1, the ridge, designated 5 in FIG. 1, which is necessary to join the box 1 and the extension 2, interferes with the conductors and terminal strip of the device as they are installed in the box.
Accordingly, it is an object of the present invention to provide an electrical junction box which will conveniently mount an alarm signaling unit and fit in the three and one-half inch stud space between a wall and a bar hanger, and yet which will provide adequate space to accommodate the speaker portion of an alarm signaling unit as well as electrical conductors for powering the unit and other devices down the line.
Another object of the present invention is to provide an electrical junction box assembly which will fit between a wall and a bar hanger, with means for mounting a grounding screw in such a way to ensure that the grounding screw will not abut the bar hanger.